Analysis of the phage typing data to date reveals: 1. That the "major" epidemic strains of S. aureus increased in the early 1960's to high levels and declined in the mid-1960's, not to reappear. 2. The world-wide epidemic strain 80/81 appeared in the Clinical Center in March of 1959, immediately spreading through the hospital and via employees, to their families. It disappeared from the Clinical Center in 1965, and has not reappeared. 3. At present there are in the Clinical Center no "epidemic types." 4. Phage typing patterns are less clearcut, particularly in the mixing of reactions of phage and from lytic groups I, II, III, and Miscellaneous.